diff -r 54dec90cbea9 xen/drivers/passthrough/vtd/dmar.c
--- a/xen/drivers/passthrough/vtd/dmar.c	Fri Jul 11 15:37:31 2008 +0100
+++ b/xen/drivers/passthrough/vtd/dmar.c	Mon Jul 14 16:56:47 2008 +0800
@@ -333,6 +333,8 @@ acpi_parse_one_rmrr(struct acpi_dmar_ent
 
     rmrru->base_address = rmrr->base_address;
     rmrru->end_address = rmrr->end_address;
+    printk("RMRR: base address = %"PRIx64", end address = %"PRIx64"\n",
+            rmrr->base_address, rmrr->end_address);
     dev_scope_start = (void *)(rmrr + 1);
     dev_scope_end   = ((void *)rmrr) + header->length;
     ret = acpi_parse_dev_scope(dev_scope_start, dev_scope_end,
diff -r 54dec90cbea9 xen/drivers/passthrough/vtd/iommu.c
--- a/xen/drivers/passthrough/vtd/iommu.c	Fri Jul 11 15:37:31 2008 +0100
+++ b/xen/drivers/passthrough/vtd/iommu.c	Mon Jul 14 16:50:49 2008 +0800
@@ -1558,10 +1558,13 @@ static int iommu_prepare_rmrr_dev(struct
                                   u8 bus, u8 devfn)
 {
     u64 size;
-    int ret;
+    int ret = 0;
 
     /* page table init */
     size = rmrr->end_address - rmrr->base_address + 1;
+    if ( size >> PAGE_SHIFT_4K <= 0 )
+        return ret;
+
     ret = iommu_page_mapping(d, rmrr->base_address,
                              rmrr->base_address, size,
                              DMA_PTE_READ|DMA_PTE_WRITE);